HIGH-RESOLUTION ROTATIONAL SPECTROSCOPY OF THE CARBON CHAIN ANIONS C$_3$N$^-$, C$_4$H$^-$, AND C$_4$D$^-$

Author Institution: Harvard-Smithsonian Center for Astrophysics, 60 Garden St.; Cambridge, MA 02138, and School of Engineering \& Applied Sciences, Harvard University, 29 Oxford St., Cambridge, MA 02138}The rotational spectra of C$_3$N$^-$, C$_4$H$^-$, and C$_4$D$^-$ have been observed at high spectral resolution by Fourier transform microwave spectroscopy. For both C$_3$N$^-$and C$_4$D$^-$, frequencies of the hyperfine components in the lowest-$J$ transitions have been determined to better than 0.1 ppm. The derived quadrapole coupling constants $eQq$ for both anions are in good agreement with theoretical predictions. A number of other properties of these anions, including linewidths and rotational temperatures, have been systematically studied with respect to similar-sized neutral molecules. The production of C$_4$H$^-$ using different hydrocarbon precursor and buffer gases has also been investigated